The leaders of the world's largest general scientific society issued an imperative climate change warning Sunday. "The atmospheric concentration of carbon dioxide, a critical greenhouse gas, is higher than it has been for at least 650,000 years. The average temperature of the Earth is heading for levels not experienced for millions of years."

Global warming is not a theory, it is a fact based on a "growing torrent of information," said the Board of Directors of the American Association for the Advancement of Science, AAAS, in its first consensus statement on climate change. The statement was issued at the association's annual meeting in San Francisco, which concludes today.

"Scientific predictions of the impacts of increasing atmospheric concentrations of greenhouse gases from fossil fuels and deforestation match observed changes. As expected, intensification of droughts, heat waves, floods, wildfires, and severe storms is occurring, with a mounting toll on vulnerable ecosystems and societies," the board said.

This photo-realistic image of the Earth was made using MODIS surface reflectance data collected and composited over the late spring and early summer of 2001. (Image by Reto Stockli courtesy NASA Earth Observatory)

Approved by the board on December 9, 2006, nearly two months before a similar statement by the Intergovernmental Panel on Climate Change, the AAAS statement warns, "Delaying action to address climate change will increase the environmental and societal consequences as well as the costs. The longer we wait to tackle climate change, the harder and more expensive the task will be."

"Accumulating data from across the globe reveal a wide array of effects: rapidly melting glaciers, destabilization of major ice sheets, increases in extreme weather, rising sea level, shifts in species' ranges, and more," the board stated.

"The pace of change and the evidence of harm have increased markedly over the last five years. The time to control greenhouse gas emissions is now."

"These events are early warning signs of even more devastating damage to come, some of which will be irreversible," warned the board.

The 14 member board includes scientists from Harvard, Yale and Princeton, the University of Michigan, University of Utah, Ohio State, Lehigh, the California Institute of Technology, and the James S. McDonnell Foundation.

Dr. John Holdren, who becomes board president today, told delegates in his presidential address, "Global climate change is real, humans are responsible for a substantial part of it, and it's taking us in dangerous directions."

President of the American Association for the Advancement of Science Dr. John Holdren delivers his presidential address to delegates at the 2007 AAAS annual meeting. (Photo courtesy AAAS)

Without swift and urgent action, he said, the problems could spiral toward disastrous, permanent changes for all of life on Earth.

"Climate change is not a problem for our children and our grandchildren - it is a problem for us. It's already causing harm," said Holdren, who serves as director of the Woods Hole Research Center, and is the Teresa and John Heinz Professor of Environmental Policy at Harvard University.

Holdren's address was a review of evidence which, taken together, shows a planet under profound stress. One of the central problems, and the most complex, he said, is ending the reliance on fossil fuels that is damaging and destabilizing the Earth's ecosystem.

The year 2005 was the hottest on record, he said. The 13 hottest years on record all have occurred since 1990. Twenty-three out of the 24 hottest years have occurred since 1980. The sort of heat wave that killed 35,000 people in Europe in the summer of 2003 is expected to become normal by 2050, he warned.

By 2100, Holdren said, some projections say global temperatures could rival those of the Eocene epoch some 35 million years ago, a time of global warming that caused waves of extinction in Earth's ecosystem.

He quoted a colleague who envisioned "crocodiles off of Greenland and palm trees in Wyoming."

But the warming temperatures do not simply make the weather warmer - they destabilize the weather and generate more extremes, Holdren said.

Some areas are getting wetter; others are experiencing unusual long-term droughts. Cyclones are becoming more powerful.

When Ethiopia's worst drought since 1984-85 hit the southern Somali region in 2000, 15,000 people found food aid, water and shelter at the Denan IDP camp in Gode zone. (Photo by Wagdi Othman courtesy WFP)

Between 1950 and 2000, he said, the number of major floods and wildfires has increased dramatically in almost every region of the world.

To address the challenges, Holdren said that world leaders would have to cooperate as never before on economic, diplomatic and technological fronts.

Such cooperation would have to yield new commitments and strategies to resolve the crushing poverty that affects perhaps two billion people - about one in every three people on Earth.

A cap on carbon emissions or a "carbon tax" to encourage use of alternative fuels is "desperately" needed, Holdren said.

In his morning media briefing and his presidential address in the evening, Holdren said solutions must be pursued across a range of disciplines - economics, science, medicine, technology, and education.

Holdren cautioned against expectations that a single technological solution such as nuclear fusion would emerge to solve energy and climate problems. Eight countries are now cooperating to build a demonstration fusion facility in France. "Belief in technological miracles," Holdren told reporters, "is generally a mistake."

Climate change research from around the world was presented at the annual meeting, which winds up today.

The Inuit people have spent thousands of years working and living in the Arctic, but climate change is forcing them to change their traditional way of doing things.

Natural Sciences and Engineering Research Council grantee Barry Smit told conference delegates the Inuit are sometimes not being given the tools they need to make the correct decisions for their lifestyles.

"We have plenty of climate change models for the Arctic, but often they do not measure the things the Inuit rely on to make the best decision on how to use their resources," says Smit, a University of Guelph researcher and the Canada Research Chair in Global Environmental Change.

Smit travels to coastal Inuit communities such as Arctic Bay, at the north end of Baffin Island, to study how the Inuit are adapting to climate change. Smit says the transfer of knowledge between the old and the young today does not happen as often as it used to, and the knowledge itself is no longer as relevant.

"A generation ago, Inuit used dogs to travel over sea ice. Now they use snowmobiles, which are faster and more convenient, but don't sense thin ice like dogs do," Smit said. "As ice becomes more unpredictable with climate change, this is becoming a serious problem. Degradation of the permafrost is affecting travel on the land and the stability of some structures."

Bridging the gap between scientific and traditional knowledge is the impetus Smit uses as part of ArcticNet, a Network of Centres of Excellence that studies the impact of climate change in the North.

At a news conference on the opening day of the meeting, Thursday, Lonnie Thompson, who has achieved global recognition for studying ice cores to learn about climate change, warned that Peru's Quelccaya, the world's largest ice cap, has lost about 22 percent of its glacial mass over the past 20 years and is retreating at 200 feet per year.

A geological sciences professor at Ohio State, Thompson said that in Peru tropical glaciers like Quelccaya store essential fresh water for consumption, agriculture and hydroelectricity.

Glacial melt also endangers communities through avalanches and floods, Thompson said, bringing an increased risk of dam breach and floods.

"The flora and fauna of mountain climates are very sensitive, both for the organisms that live in them, and the communities that depend on them," said Professor John David All, a specialist in geography, global climate change and international environmental law at Western Kentucky University.

Organizer and moderator of a related symposium on mountains and climate change, All said that mountain communities must adapt to the changing climate.

"In California, the increase in glacial melt changes the runoff season. In some places, it occurs in February or March - too early for the growing season," said All. "When you get hooked on high water runoff, and then it dies, it is bad if you have not prepared."

All added that melting snow pack on Mount Kilimanjaro in Africa has the potential to affect Tanzanian tourism, the nation's largest industry. "Would you invest in hotels if you know the snow was melting?" he asked.

Henry Diaz, climate researcher with the U.S. National Oceanic and Atmospheric Administration, is concerned that human implications of changing mountain environments are not widely understood.

Diaz has recorded a two degree Fahrenheit rise in temperature since the mid-1970s in Western mountains of the United States. This has caused snowmelt and flowering of trees to occur about two weeks earlier than 50 years ago.

"The issue is ignored, but demands on mountains are high and snow pack have clear economic and social impacts," said Diaz. "The message is not getting out because mountains are under-instrumented and the information is scattered among different experts."

Citing shrinking tropical glaciers on mountains in the Andes, Himalayas, and on Kilimanjaro, Thompson warned that many show evidence of the disappearance of glacial mass that accumulated over 5,000 years.

Even if we stopped producing greenhouse gases immediately, Thompson said, we would not see an immediate benefit because "there are still some gases and energy stored in the system."